Kinetics of the glucose/glycine Maillard reaction pathways: influences of pH and reactant initial concentrations

A previously proposed kinetic model for the glucose/glycine Maillard reaction pathways has been validated by changing the initial pH (4.8, 5.5, 6.0, 6.8 and 7.5) of the reaction and reactant initial concentrations (1:2 and 2:1 molar ratios were compared to the 1:1 ratio). The model consists of 10 steps, each characterised by a rate constant. The initial pH had a different effect on the various rate constants, and the results suggest a mixture between specific acid and base catalysis. pH–rate profiles were established and, from these, a quantitative relationship was derived: kobs = ke(10pD × pH), in which kobs is the estimated rate constants from experiments, ke an expression for the elementary reaction, and pD the parameter describing the pH-dependence. The parameters ke and pD were estimated from the pH–rate profiles. This equation thus expresses the pH-dependence of rate constants in much the same way as the Arrhenius equation does for the temperature-dependence of rate constants. The initial concentrations of glucose and glycine did not have an effect on the estimated rate constants, indicating that the model is robust to change in initial concentrations of the reactants. Finally, a sensitivity analysis of the model was performed to highlight the important steps, as well as finding possible redundant ones. Again, the model performed well; all steps were important and the model was consistent with the established reaction mechanism.